bio17

Biology, 6th Edition

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Greg Steinberg AP Biology Chapter 17 From Gene to Protein A. The Connection Between Genes and Proteins a. Metabolic Defects are evidence that genes specify proteins. i. Archibald Garrod was the first to suggest that genes affect phenotypes by enzymes. ii. Garrod used alkaptonuria as an example, saying that it is an enzyme that is produced by inherited genes that breaks down the chemical that causes the disease. b. How Genes control metabolism i. Biochemists discovered that most cell activity goes through metabolic pathways regulated by enzymes. ii. Some metabolic pathways lead to things such as eye pigment in Drosophila. iii. George Beadle and Edward Tatum worked with a bread mold called Neurospore Crassa. iv. The mutant of this mold cannot sustain life on the normal minimum needs of the wild type. This is because the mutant mold is missing key enzymes and proteins that are needed in order to convert the minimum molecules to needed molecules. v. Beadle-Tatum also worked with arginine requiring mold. Each mutant fell into 1 of three classes; they claimed they could identify the requirements of each mutant by determining what class they fell into. c. One Gene-One Polypeptide i. Not all proteins are enzymes. ii. Biologists thought that 1 gene made 1 protein. But they later determined that 1 gene forms 1 polypeptide, since most proteins are made up of 1 or more polypeptides. d. Transcription and Translation – Pathways to polypeptides i. Genes do not code for proteins directly. It is RNA that bridges the gap between DNA and proteins. ii. RNA is similar to DNA except it uses the sugar Ribose instead of Deoxyribose and replaces Thymine with Uracil. iii. The 4 nucleotides are the monomers of DNA or RNA. Genes have hundreds or thousands of nucleotides. The polypeptide uses the 20 amino acids as its monomers. Both polypeptides and DNA/RNA is written in two different languages, and need to be converted to get to one from the other. e. Transcription i. Transcription is when RNA is synthesized by DNA.
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ii. RNA and DNA are in the same language and simply, DNA needs only to be transcribed to RNA and not translated. iii. DNA provides the original copy to be translated into RNA.
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